There is conventionally known an electrophotographic type image forming apparatus including a main frame and a process cartridge detachably mountable in the main frame.
For example, there is proposed a process cartridge integrally having a photosensitive drum and a developing unit including a developing roller, and the process cartridge is detachably attached to a main frame of an image forming apparatus in an axial direction of the photosensitive drum.
Service life of such process cartridge generally depends upon the service life of the developing unit which is comparatively shorter than that of the photosensitive drum.
In the above image forming apparatus, since the process cartridge integrally has the photosensitive drum and developing unit, both the photosensitive drum and developing unit need to be replaced simultaneously when the service life of the developing unit is reached. Thus, there is a limit in reduce running cost.
Thus, there is a demand to develop an image forming apparatus in which a developing unit can be detachably attached to a main frame independently of a photosensitive member.
In such an image forming apparatus, in order to prevent interference between a developing roller and the photosensitive member during attachment and detachment of the developing unit relative to the main frame, the developing unit needs to movable between a position at which the developing roller and photosensitive member contact each other (contact position) and a position at which the developing roller and photosensitive member are separated from each other (separation position).
As such image forming apparatus in which the developing unit is configured to be movable in this manner, there is proposed an electrophotographic copier whose main frame (copier body) is provided with a photosensitive belt and a guide rail configured to be movable with respect to the main frame. A developing unit is configured to be attached/detached relative to the main frame while being guided by the guide rail. Moving the guide rail in a state where the developing unit has been attached to the main frame permits the developing unit to move between the contact position and the separation position.
In this electrophotographic copier, the developing unit is attached to/detached from the main frame when the developing unit is at the separation position.